As a cleaning method of a surface of a substrate such as a semiconductor wafer, for example, a wet type substrate cleaning method is commonly used. In the wet type substrate cleaning method, foreign materials are removed by immersing a target substrate in a solution or solvent, or by spraying a solution or solvent to the substrate. Then, the substrate is rinsed with pure water, if necessary.
In the wet type substrate cleaning method, the solution residues or solvent residues remaining on the surface of the substrate after cleaning may cause water marks, surface oxidation, and the like. Accordingly, for example, the solution residues, the pure water residues, and the like are dried and removed by performing a spin dry process after the immersion or spray cleaning process.
For example, Japanese Patent Publication No. 2008-41873 discloses a conventional substrate cleaning method including, a first step of cleaning a surface of a substrate with a liquid chemical, a second step of substituting pure water for liquid chemical residues remaining on the surface of the substrate, a third step of treating the surface of the substrate with hot pure water having a temperature higher than that of the pure water used in the second step, a fourth step of cooling the substrate to a temperature lower than that of the hot pure water, and a fifth step of drying the substrate after cooling.
However, in the wet type substrate cleaning method using the liquid chemical, when the liquid including the liquid chemical is volatilized in the dry process after cleaning, a pattern formed on the surface of the substrate collapses due to gas-liquid interface tension. Specially, when the dry process uses sublimation of dry ice such as Ar and CO2, the pattern collapse gets more serious.
Further, pattern collapse occurs in even a pattern having a size of 70 to 60 nm, and it may be very difficult to prevent a pattern having a size of about 20 nm and an aspect ratio of about 10 from collapsing after wet cleaning. In case of a target substrate having a so-called low-k film, liquid may infiltrate into a porous portion of the low-k film and it is difficult to completely remove the liquid that has already infiltrated into the porous portion. Accordingly, it is preferable to avoid adopting the wet type substrate cleaning method.